1. Field of the Invention
The present invention relates generally to internal combustion engines and more specifically to a throttle valve control arrangement for controlling the engine speed during idling thereof.
2. Description of the Prior Art
FIG. 1 of the drawings shows an arrangement disclosed in Japanese Patent Application First Provisional Publication No. 57-195831/1964. This arrangement includes an engine idle control arrangement wherein the position of the engine throttle valve 1 is modified via the provision of a servo device. As shown this device includes a vacuum motor 3, the vacuum chamber 4 of which is selectively supplied vacuum from the induction passage 5 via a solenoid controlled valve 6. In the illustrated arrangement the vacuum motor includes a diaphragm 7 which partitions a housing 8 into the above mentioned vacuum chamber 4 and an ambient pressure chamber 9 and which has a stopper rod 10 connected thereto. This rod 10 is arranged to cooperate with an adjust lever 11 which is connected to the shaft (no numeral) of the throttle valve. With this arrangement upon vacuum being supplied to the vacuum chamber 4 the diaphragm 7 flexes in a manner to pull the rod 10 and thus rotate the throttle valve 1 by a predetermined small amount. Upon the level of vacuum falling toward atmospheric a return spring 12 disposed in the vacuum chamber 4 pushes the rod 10 to the left as seen in the drawings and thus permits the throttle valve 1 to assume a more restrictive position.
The solenoid valve 6 includes a valve seat 13 and valve element 14. That latter mentioned element 14 is moved under the control of a solenoid 15. An orifice 16 of a predetermined diameter is disposed so as bleed air into the passage 17 which interconnects the solenoid valve 6 and the vacuum chamber 4. The time for which the valve is open and vacuum from the induction passage 5 permitted to be supplied to the vacuum chamber 4 is determined in accordance with the duty cycle of the signal via which the solenoid 15 is energized. In this arrangement the valve element is fully opened when the duty cycle is 100% and fully closed when the duty cycle is 0%. At values between these two limits the amount of vacuum which is supplied to the vacuum chamber is modulated by the open and closing timing of the valve and the diameter of the air-bleed.
The solenoid 15 is operatively connected with a control arrangement which includes a control circuit 16 (including a microprocessor--by way of example) which is supplied data from an engine speed sensor 17, a vehicle speed sensor 18 and an engine coolant temperature sensor 19. In accordance with this data a suitable duty cycle valve is determined.
With this arrangement when the engine temperature is relatively high the duty cycle is lowered as compared with the fixed value which is used when the engine temperature is below an predetermined value.
Interposed between the control circuit 16 and the solenoid 15 are two switches 17, 18 which are arranged in parallel. The first of these switches (17) is arranged to be closed when a transmission associated with the engine (not shown) controlled by the instant device is conditioned to assume a neutral gear while the second switch (18) is connected with a clutch which provides a drive connection between the engine and the transmission. This second switch 18 is arranged to assume a closed position when the clutch assumes a condition wherein rotational energy between the engine and the transmission is not transmitted.
Thus, when either of switches is closed the solenoid 15 and the control circuit 16 are operatively connected.
However, this arrangement suffers from the drawback that when the engine stops oily residues which tend to collected in the induction passage 5 find their way into conduit 19 and eventually reach the valve seat 13 During the same time small amounts of dust and the like tend to enter the valve via the orifice 16. These small soil particles in combination with the sticky residue which has reached the valve seat 13 form a mass which when warm is relatively plastic but which when cool hardens and forms a gum which tends to "glue" the valve element to the valve seat.
When the engine is subject to a cold start, as the duty cycle of the signal which is applied to the solenoid 15 is low the amount of force produced by the solenoid is relatively low and is often insufficient to pull the valve element free 14 of the valve seat 13. Under these conditions vacuum cannot be supplied to the vacuum chamber 4 and the idling control is prevented.